1. Field of the Invention
This invention relates to stepper motors, and in particular to a stepper motor which uses a composite magnet.
2. Description of Related Art
U.S. Pat. No. 4,207,483, issued to Baer, discloses an electric stepper motor using a rotor having embedded permanent magnets which are polarized in an axial direction. Energizing one of two coils associated with two stator members causes the rotor to move one detent position.
One major drawback in this motor is the difficulty in manufacturing the rotor. Baer teaches that twelve permanent magnet regions are equally spaced around the circumference of a ceramic ring which is affixed to the hub of the motor. For optimal performance, the centers of the permanent magnet regions are located at the same radial position from the motor axis as the radial centers of the stator pole teeth. For these conditions to be met, precise tooling of all twelve permanent magnet regions, as well as the ceramic ring, is required. Moreover, assembly of the permanent magnet regions into the ceramic ring is time and labor intensive.
Therefore, a need arises for a stepper motor having a rotor which provides well-definced poles as well as ease of manufacture at a reasonable cost.